Power steering - whining noise on 2002 Chrysler PT Cruiser

This past summer my steering had a whining/grinding noise. Every time I turned the steering wheel it had this loud, high-pitched grinding sound. My steering, however, was just fine, no problems. As it got colder the noise got louder. It would be loudest in the morning when the car first started up, and then would quiet down (but never completely disappear) after the car warmed up.
Then we had a few days where it was extremely cold, and when I drove the car in the morning I would have no noise but it would be really hard to steer. After a few seconds of turning the wheel the noise would come back and it would be easy to steer again. Now, there is no noise but it's extremely hard to steer all the time, no matter what the temperature is or how long the car has been on.